Geology topics

Research about Lake Spokane

Source-linked reports with geographic coverage including Lake Spokane.

3 recordsLinked to original sources

USGS2021

Nitrogen and phosphorus loads from groundwater to Lake Spokane, Spokane, Washington, October 2016–October 2019

Shallow nearshore groundwater and estimates of groundwater seepage were collected at 21 locations along the north and south shores of Lake Spokane beginning in October 2016 and ending in October 2019. Nitrate plus nitrite concentrations in nearshore groundwater ranged from <0.04 to 7.60 milligrams of nitrogen per liter. Nearshore groundwater orthophosphate concentrations ranged from <0.004 to 0.381 milligrams of phosphorus per liter, and, overall, there were no consistent seasonal differences in nearshore groundwater nutrients during this study. Nitrate plus nitrite concentrations were highest at sites located adjacent to nearshore development and similar to concentrations in water collected from nearby drinking water wells. Similarly, samples from locations adjacent to nearshore development were statistically greater than samples collected from other locations for orthophosphate concentrations. Dissolved boron concentrations, elevated values of which are an indicator of household-detergent use, were elevated in spring and summer at some locations, indicating that residential wastewater was reaching the lake. Stable isotope ratios of nitrate ( 15 N and 18 O), which were used to identify the source nitrate in sampled groundwater, showed that most data indicated a mix of soil nitrogen and nitrogen sources from human or animal waste. Generally, median groundwater discharge to the lake was low across all sites and seasons, with most values smaller than 1 centimeter per day (cm/d). Similar to the nutrient-concentration data, seasonal patterns in seepage flux were weak, and, where there were seasonal increases in flux, the increased groundwater discharge did not carry increased nutrients. Localized estimates of groundwater seepage flux were scaled up to the entire length of the lakeshore. The median groundwater flux of 0.34 cm/d scaled to 1.9 cubic feet per second (ft 3 /s) and the maximum recorded seepage flux of 17.6 cm/d was equivalent to 97 ft 3 /s. These estimates of groundwater inputs are orders of magnitude less than surface water inputs to the lake. Nutrient loads were determined from the product of groundwater flow and a representative nutrient concentration. Using the median seepage flux of 1.9 ft 3 /s, the orthophosphate load ranged from 0.7 to 3.8 pounds of phosphorus per day based on the median and maximum orthophosphate concentrations, respectively. For nitrate plus nitrite, loads ranged from 5.8 to 76.6 pounds of nitrogen per day. Using the maximum value of seepage flux, maximum orthophosphate loads ranged from 35 to 198 pounds of phosphorus per day, and maximum nitrate plus nitrite loads ranged from 296 to 3,943 pound of nitrogen per day. Overall, groundwater nutrient loads are small compared to other sources to the lake. Continued monitoring of future nutrient loads would aid decisions by resource managers as infrastructure within the neighboring residential communities continues to age around Lake Spokane.

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USGS2019

Population characteristics and the potential suppression of common carp in Lake Spokane, Washington

Common Carp Cyprinus carpio is a nonnative species that often has deleterious effects on aquatic systems. As such, there is interest in suppressing nonnative Common Carp populations in areas where humans have introduced them. The objectives of this study were to 1) provide insight on efficient techniques for capturing Common Carp, 2) describe their population demographics and dynamics, 3) evaluate whether temperature and water elevation were related to growth and recruitment, and 4) develop an age-structured population model for evaluating different management scenarios of Common Carp removal in Lake Spokane, Washington. Catch rates of Common Carp varied among sampling gears with slightly higher catch rates in monofilament (mean ± SD; 15.5 ± 9.8 fish/net night) vs. multifilament (12.7 ± 7.3 fish/net night) gill nets. Catch rates of Common Carp with nighttime electrofishing (0.3 ± 0.4 fish/min) were higher than daytime electrofishing (0.1 ± 0.2 fish/min). Common Carp in Lake Spokane exhibited variable recruitment, rapid growth, large-length structure, high longevity (i.e., age 18 y), and low total annual mortality (17.0%). Air temperature was positively associated with annual growth increments ( R 2 ≤ 0.25). Neither air temperature nor water elevation was highly correlated ( R 2 ≤ 0.20) to recruitment of Common Carp. A Beverton–Holt yield-per-recruit model suggested that yield declined with increasing exploitation. Recruitment overfishing would occur at exploitation rates of 20–40% for all targeted minimum length categories (i.e., 150, 300, 450 mm) except 600 mm. Results from this study provide important information on the ecology of Common Carp that can be used to guide management efforts (e.g., suppression) in western systems.

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USGS2016

Preliminary characterization of nitrogen and phosphorus in groundwater discharging to Lake Spokane, northeastern Washington, using stable nitrogen isotopes

Lake Spokane, locally referred to as Long Lake, is a 24-mile-long section of the Spokane River impounded by Long Lake Dam that has, in recent decades, experienced water-quality problems associated with eutrophication. Consumption of oxygen by the decomposition of aquatic plants that have proliferated because of high nutrient concentrations has led to seasonally low dissolved oxygen concentrations in the lake. Of nitrogen and phosphorus, the two primary nutrients necessary for aquatic vegetation growth, phosphorus was previously identified as the limiting nutrient that regulates the growth of aquatic plants and, thus, dissolved oxygen concentrations in Lake Spokane. Phosphorus is delivered to Lake Spokane from municipal and industrial point-source inputs to the Spokane River upstream of Lake Spokane, but is also conveyed by groundwater and surface water from nonpoint-sources including septic tanks, agricultural fields, and wildlife. In response, the Washington State Department of Ecology listed Lake Spokane on the 303(d) list of impaired water bodies for low dissolved oxygen concentrations and developed a Total Maximum Daily Load for phosphorus in 1992, which was revised in 2010 because of continuing algal blooms and water-quality concerns. This report evaluates the concentrations of phosphorus and nitrogen in shallow groundwater discharging to Lake Spokane to determine if a difference exists between nutrient concentrations in groundwater discharging to the lake downgradient of residential development with on-site septic systems and downgradient of undeveloped land without on-site septic systems. Elevated nitrogen isotope values (δ 15 N) within the roots of aquatic vegetation were used as an indicator of septic-system derived nitrogen. δ 15 N values were measured in August and September 2014 downgradient of residential development near the lakeshore, of residential development on 300-ft-high terraces above the lake, and of undeveloped land in the eastern (upper) and central (lower) parts of Lake Spokane. Significantly lower δ 15 N values were measured within aquatic vegetation downgradient of undeveloped land in eastern Lake Spokane relative to both near-shore and terrace residential development land uses. Conversely, significantly higher δ 15 N values were measured downgradient of undeveloped land in central Lake Spokane relative to the two developed land uses. These results guided the location of subsequent groundwater sampling in March and April 2015 from 30 shallow piezometers driven into the near-shore area of Lake Spokane. Nitrate plus nitrite concentrations in groundwater discharging to Lake Spokane downgradient of undeveloped areas were significantly lower than those measured downgradient of both near-shore and terrace residential development. Orthophosphate concentrations in groundwater were not significantly different with respect to upgradient land use.

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